Currently known membranes of this type have a surface which generally includes irregularities in the form of depressions and projections on a microscopic scale which lead to the following drawbacks:
(1) when using the membrane in direct filter mode, the interface between the membrane and the filter cake is irregular in shape and thus makes it more difficult to clean the surface of the filter when unclogging it; and
(2) when using the membrane in tangential filter mode, the tangential flow which is intended to prevent a filter cake from forming by washing away particles which are stopped at the pore inlets, is incapable of washing away particles trapped at pore inlets which are situated in the bottoms of depressions. Further, the particles being washed away tangentially are washed up against surface projections, thereby building up collections of particles on the upstream side of such projections and thus beginning the formation of a filter cake.
The depressions and projections on the surface of the membrane thus reduce the overall permeability of the membrane and make it necessary to unclog the membrane more frequently, thereby complicating the use of the filter.
Preferred implementations of the present invention mitigate these drawbacks by providing a filter membrane which clogs up relatively slowly, which can be quickly and easily unclogged, eg. by applying reverse pressure, and which can be used for filtration or ultrafiltration of very hot and/or corrosive liquids or gases.